Power line communications (PLC) technology is aimed at transmitting digital data by utilizing the existing infrastructure of the electrical grid. It allows, in particular, remote reading of electric meters, exchanges between electric vehicles and the recharging terminals and also management and control of energy networks (smart grid). PLC technology incorporates, in particular, narrow band power line communication (N-PLC) which is generally defined as a communication over an electrical line operating at transmission frequencies of up to 500 KHz. N-PLC communication thus generally uses the frequency bands defined in particular by the European committee for electrotechnical standardization (CENELEC) or by the Federal Communications Commission (FCC). Thus, if the CENELEC A frequency band (3-95 kHz) is considered, the transmission frequencies are situated between 35.9375 and 90.625 KHz for the PLC-G3 standard.
The overall performance of a receiver depends on the quality of its channel estimation, i.e. on the estimation of the transfer function of this channel. It is known that a transmission channel can vary in time, in frequency, in phase and in amplitude. Moreover, the signals conveyed by power line communications and received by the receiver result from a combination of several signals having followed within the transmission channel (i.e. the electrical line) several propagation routes or paths, each having its own time delay and its own attenuation (i.e. the transmission channel is a multi-path transmission channel). This may then result in strong attenuation of certain frequencies.
Moreover, the properties and characteristics of the electrical networks are not known and may vary over time. Thus, the impedances of certain objects plugged in by the user vary with the voltage. Such is the case, for example, with halogen lamps or objects comprising voltage rectifiers. When a user plugs in such objects, it results in a periodic variation of the transfer function of the transmission channel. The channel is then considered to be linear and cyclostationary or “linear and varying temporally in a periodic manner”, this corresponding to the acronym LPTV (“Linear Periodically Time Varying”).
Contemporary receivers, compatible with the PLC-G3 standard, are not suitable for performing channel estimations when the channel is time varying. Indeed, the PLC-G3 standard provides for the use of only two orthogonal frequency-division multiplexing (OFDM) symbols as pilot symbols to fully estimate the transfer function of the channel. Hence, when the channel varies, and in particular, when a cyclostationary channel is present, channel estimation may be erroneous, or perhaps impossible, and consequently potentially leads to errors in decoding the symbols.